Ii-iii-n semiconductor nanoparticles and method of making same

ABSTRACT

The present application provides nitride semiconductor nanoparticles, for example nanocrystals, made from a new composition of matter in the form of a novel compound semiconductor family of the type group II-III-N, for example ZnGaN, ZnInN, ZnInGaN, ZnAlN, ZnAlGaN, ZnAlInN and ZnAlGaInN. This type of compound semiconductor nanocrystal is not previously known in the prior art. The invention also discloses II-N semiconductor nanocrystals, for example ZnN nanocrystals, which are a subgroup of the group II-III-N semiconductor nanocrystals. 
     The composition and size of the new and novel II-III-N compound semiconductor nanocrystals can be controlled in order to tailor their band-gap and light emission properties. Efficient light emission in the ultraviolet-visible-infrared wavelength range is demonstrated. 
     The products of this invention are useful as constituents of optoelectronic devices such as solar cells, light emitting diodes, laser diodes and as a light emitting phosphor material for LEDs and emissive EL displays.

FIELD OF THE INVENTION

This invention relates to nitride semiconductor nanoparticles, forexample nanocrystals having nanometre dimensions, and in particular tosuch materials in a new compound semiconductor system of the type groupII-III-N. Such materials can be used in a wide range of applicationsincluding solar cells, light emitting diodes, emissive EL displays andbio-imaging.

BACKGROUND OF THE INVENTION

Semiconductor nanocrystals whose dimensions are comparable to the bulkexciton diameter show quantum confinement effects. This is seen mostclearly in the optical spectra which shift to blue wavelengths as thesize of the crystal is reduced.

A compound semiconductor is a semiconductor material composed ofelements from two or more groups of the periodic table. These elementscan form binary (2 elements), ternary (3 elements), quaternary (4elements) or penternary (5 elements) compounds. The most common familiesof compound semiconductors are III-V (e.g. GaAs, AlGaAs, GaN, GaInP) andII-VI (e.g. ZnS, CdTe, ZnO). But, numerous other compound semiconductorfamilies have been studied (e.g. I-VII, IV-VI, V-VI, II-V etc). Acomprehensive source of the basic data of known inorganic semiconductorsis contained in Semiconductors: Data Handbook by Madelung,Springer-Verlag press; 3rd ed. edition (November 2003).

Semiconductor nanocrystals made from a wide range of materials have beenstudied including many II-VI and III-V semiconductors. II-Vsemiconductor compounds such as ZnN and ZnAs are known [Paniconi et al.J. Solid State Chem 181 (2008) 158-165] and [Chelluri et al. APL 49 24(1986) 1665-1667] in the form of thin films or powders. Fornanocrystals, [Buhro et al. Polyhedron Vol 13. (1994) p 1131] report onthe synthesis of ZnP nanoparticles.

III-V semiconductors are numerous and one of the most interestingclasses of III-V semiconductors is the III-nitrides, such as AlN, GaN,InN and their respective alloys. These are used for the manufacture ofblue light-emitting diodes, laser diodes and power electronic devices.Nitrides are also chemically inert, are resistant to radiation, and havelarge breakdown fields, high thermal conductivities and large high-fieldelectron drift mobilities, making them ideal for high-power applicationsin caustic environments [Neumayer at. al., Chem., Mater., 1996, 8, 25].The band gaps of aluminum nitride (6.2 eV), gallium nitride (3.5 eV) andIndium nitride (0.7 eV) [Gillan et. al., J. Mater. Chem., 2006, 38,3774] mean that nitrides span much of the ultraviolet, visible andinfrared regions of the electromagnetic spectrum. The fact that alloysof these materials have direct optical band gaps over this range makesthese very significant for optical devices.

Solid-solution GaN/ZnO nanocrystals have been reported [Han et al. APL.96, (2010) 183112] and were formed by combining GaN and ZnO nanocrystalsas a crystal solid. The ratio of ZnO to GaN was controlled by varyingthe nitridation time of a GaZnO precursor.

III-IV-V semiconductors, for example SiGaAs, have been reported in thinfilm form (for example in U.S. Pat. No. 4,213,781), but have not beenreported not in nanoparticle form.

F. Zong et al. propose, in “Structural properties and photoluminescenceof zinc nitride nanowires”, Applied Physics Letters (8691034 IEE INSPEC,2005) and in “Nano-structures and properties of zinc nitride prepared bynitridation technique”, Proceedings of Fifth Pacific Rim InternationalConference on Advanced Materials and Processing”, Beijing, 2004 (8418308IEE INSPEC), the synthesis of zinc nitride nanowires by reacting zincpowder with ammonia gas. By a “nanowire” is meant a structure in whichtwo dimensions are of the order of nanometres and the third dimension ismuch larger, typically of the order of micrometres.

US 2009/0121184 proposes a “hydrogen storage material”, which can storehydrogen and release it when the material is heated. The materialcontains a mixture and a reaction product of a metal hydride and a metalamide.

US 2003/167778 proposes a nanostructure that contains hydrogen, forexample for use in a hydrogen storage system. It lists magnesium nitrideas a possible material, and suggests milling the material such that theresulting material “will contain some nanostructured storage material”.

Y Ye et al. propose an amorphous zinc oxynitride semiconductor material,in “High mobility amorphous zinc oxynitride semiconductor material forthin film transistors”, Applied Physics Letters (10930195 IET INSPEC,2009).

U.S. Pat. No. 6,527,858 proposes the fabrication of a ZnO singlecrystal, by a process in which atomic zinc and oxygen are supplied to agrowth chamber, together with atomic nitrogen (as a p-type dopant) andatomic gallium (as an n-type dopant).

SUMMARY OF THE INVENTION

A first aspect of the invention provides a semiconductor nanoparticlecomposed of a compound having the formula II-N or II-III-N, where IIdenotes one or more elements in Group II of the periodic table, and IIIdenotes one or more elements in Group III of the periodic table

By a “nanoparticle” is meant a particle having three dimensions that arenanoscale dimensions, for example of the order of 1 to 100 nm and morepreferably of the order of 1 to 30 nm. A nanoparticle of the inventionmay have a crystalline or polycrystalline structure and so form ananocrystal, or it may have an amorphous structure.

Where the semiconductor nanoparticle is composed of a compound having nomore than one constituent element in either Group II or Group III, thesemiconductor nanoparticle is composed of a compound having the generalII_(x)-III_(y)-N_(z), wherein x and z are greater than zero, y is equalto or greater than zero, and x, y and z give the relative quantities ofthe elements in the alloy and are set so as to balance the stoichiometryand electrical charge. More generally, a semiconductor nanoparticle ofthe invention is composed of a compound having a formula of thefollowing general form: IIa_(x1)IIb_(x2) . . . IIIa_(y1)IIIb_(y2) . . .N_(z) where IIa, IIb . . . correspond to different group II elements,IIIa, IIIb . . . correspond to different group III elements, the numbersx1 and z are greater than zero, the numbers x2 . . . , y1, y2 . . . aregreater than or equal to zero, and the numbers x1, x2 . . . y1, y2 . . .and z give the relative quantities of the elements in the alloy, and areset so as to balance the stoichiometry and electrical charge.

For convenience, the numbers x, y, z or x1, x2 . . . y1, y2 . . . and zwill generally be omitted from formulae given herein.

The present invention provides a new composition of matter in the formof a compound semiconductor nanocrystals (or more generallynanoparticles) family of the type group II-III-N or II-N. Nanocrystals(or nanoparticles) made from the compound semiconductor of the II-III-Nfamily or from a compound semiconductor of the II-N family are not knownto have been made or studied previously.

US2007/0104865 lists many possible materials for nanocrystals includingmany possible II-V materials. ZnN nanocrystals are included in the listgiven in US2007/0104865, but the manufacture of ZnN nanocrystals is notdemonstrated in US2007/0104865.

Doping of III-V semiconductors with a group II element (e.g. Mg) or IVelement (e.g. Si) is typically used to change its electricalconductivity. However, the tiny amount of group II element typicallyneeded to dope a III-V semiconductor does not lead to the formation ofan II-III-V compound [see Pankove et al. J. Appl. Phys. 45, 3, (1974)1280-1286]. As an example, U.S. Pat. No. 3,660,178 proposes diffusingelemental zinc into a III-V compound semiconductor, but the amount ofdiffused zinc is classified as an impurity. An impurity amount issignificantly less than that needed to form a compound. The formation ofa II-III-V compound is not disclosed or even proposed in U.S. Pat. No.3,660,178.

In this connection it should be understood that in a nanoparticle of aII-III-V compound of the invention, the group II element(s), the groupIII element(s) and the group V element(s) are each incorporated into thecrystal structure of the compound. That in, in a ZnInN or MgInNnanoparticle of the invention, for example, the Zn or Mg atoms, the Inatoms and the N atoms are all arranged regularly in the ZnInN crystalstructure. In contrast, in prior cases where a group II element such asZn is used as a dopant in a III-V compound (as in U.S. Pat. No.3,660,178), the group II element is present in very small amounts(compared to the amounts of group III element or group V element) andthe group II element is not properly incorporated in to the crystalstructure of the III-V compound—so that the result is a group III-Vcompound that contains a small amount of a group II impurity. As ageneral rule, a nanoparticle of a II-III-V compound of the presentinvention will contain at least 1% by volume of each of the group II,III and V element atoms—whereas, when a group II element is used as adopant in a III-V compound, the compound will contain much less than 1%of the group II element.

Similarly, a nanoparticle of a II-N compound is defined as containing atleast 1% by volume of each group II and N element atoms.

In the field of III-V semiconductor nanocrystals, the formation ofnanocrystals of semiconductors with the formula ABC is proposed in U.S.Pat. No. 7,399,429, where A is group II, III or IV, B is group II, IIIor IV and C is group V or VI [paragraph 5]. However, the actualformation of nanocrystals of a compound having the specific formulaII-III-N is not reported nor even specifically proposed.

US2008/0202383 discloses the formation of nanocrystals made from theI-II-III-VI semiconductor alloy. The formation of II-III-N or II-Nnanocrystals is however not disclosed.

In the field of III-nitride semiconductor nanocrystals, UK patentapplication 0901225.3 describes emissive nitride nanocrystals in whichzinc stearate is used as a capping agent during the synthesis of III-Nnanocrystals. This application proposes that the zinc stearate moleculesare coordinated onto the surface of the III-nitride nanocrystals andpassivate the nitrogen atoms at or near the surface of the III-nitridenanocrystal, and does not show or state that a II-III-N nanocrystal or aII-N nanocrystal is formed.

The II-III-N compound semiconductor nanocrystals may comprise a materialcontaining:

-   -   one or more group II elements from the periodic table—for        example, Zn, Cd, Hg, Be, Mg, Ca, Sr, Ba, Ra;    -   one or more group III elements from the periodic table—for        example, Ga, In, Al, B, Tl;    -   and the element nitrogen

This invention discloses group II-III-N semiconductor nanoparticles, forexample nanoparticles of material families such as Zn-III-N or Mg-III-N,for example ZnGaN, ZnInN, ZnInGaN, ZnAlN, ZnAlGaN, MgInN, ZnAlInN andZnAlGaInN nanoparticles. These type of compound semiconductornanocrystals are not known in the prior art.

The II-III-V compound semiconductor nanoparticle may comprise a II-Vsubset containing:

-   -   one or more group II elements from the periodic table—for        example, Zn, Cd, Hg, Be, Mg, Ca, Sr, Ba, Ra;    -   and the element nitrogen.

This invention also discloses a II-N semiconductor nanocrystals subgroupof the group II-III-N semiconductor nanocrystals, for example ZnN orMgN. These type of compound semiconductor nanocrystals are not known inthe prior art.

A II-III-N or II-N nanoparticle of the invention has potentially manyapplications. The band gap energy or energy gap of a semiconductor isdefined as the minimum room temperature energy gap between the valenceband and conduction band of a semiconductor material. It is expectedthat the present invention will make possible the fabrication ofnanoparticles of group II-III-N or II-N semiconductor compounds havingan energy gap anywhere in the range from 0.6 eV to 6.2 eV, depending onboth the composition of the II-III-N or II-N material (which affects theband gap energy of a bulk sample of the II-III-N or II-N material) andby the nanoparticle dimensions. The desired band gap energy will dependon the intended application of the group II-III-V semiconductorcompound, but one important application of the invention is expected tobe the fabrication of compounds having energy band gaps in the range 0.6eV to 4.0 eV—this is the range required by a material to absorb almostthe entire solar spectrum for use in very high efficiency solar cells.

The first II-N or II-III-N compound may be single crystal in structure,may be polycrystalline in structure or may be amorphous in structure.

The first II-N or II-III-N compound may form a core of the nanoparticleand the nanoparticle further may further comprises a layer disposedaround the core and composed of a semiconductor material having adifferent composition to the first II-N or II-III-N compound. Thisprovides a nanoparticle having a “core-shell” structure

The shell may be composed of a second II-N or II-III-N compound, thesecond II-N or II-III-N compound having a different composition to thefirst II-N or II-III-N compound.

Alternatively, the invention may be used to provide a II-N or II-III-Nshell of a core-shell nanoparticle structure where the core is composedof a material other than a II-N or III-N material.

In a core-shell nanoparticle structure, where the core or shell isformed of a II-N or II-III-N material in accordance with the inventionit can in principle be formed of any II-N or II-III-N material.Preferably however the materials for the core and the shell are selectedsuch that the shell has a band-gap that is larger than the band-gap ofthe core in order to confine electrical charge carriers within the core,as this is expected to enhance the PLQY of the nanoparticle. The shellalso acts as protection layer around the core, preventing oxidation ofthe core.

The semiconductor nanoparticle may be light emissive. By a“light-emissive” material is meant a material that, when illuminated bya suitable exciting light source, emits light. One measure of whether amaterial is light-emissive is its “photoluminescence quantum yield”(PLQY)—the PLQY of a semiconductor material is the ratio, when thematerial is illuminated by an exciting light source to cause thematerial to photoluminesce, of the number of photons emitted by thematerial to the number of photons absorbed by the material. (It shouldbe noted that the term “photoluminescence quantum yield” should not beconfused with the term “photoluminescence quantum efficiency” which issometimes used in the art. The “photoluminescence quantum efficiency”takes into account the energy of the photons which are absorbed andemitted by a material. In cases where the excitation and emissionwavelengths are similar the photoluminescence quantum yield andphotoluminescence quantum efficiency will have similar values; howeverin cases where the excitation wavelength is shorter and hence of higherenergy than the emission wavelength the photoluminescence quantumefficiency will be lower than the photoluminescence quantum yield.)

For the purposes of this application, a “light-emissive” material willbe defined as a material having a PLQY of 1% or greater.

A light-emissive nanoparticle of the invention may have aphotoluminescence quantum yield of at least 5%, preferably of at least20%, and more preferably of at least 50%.

The present group II-III-N semiconductor nanoparticles possessremarkable luminescent properties particularly in the visible region ofthe electromagnetic spectrum. Nanoparticles of such material readilyexhibits PLQY values above 10%, and as high as 55% in the case of ZnAlNnanoparticles.

Nanoparticles of this invention are useful as a constituent ofoptoelectronic devices such as solar cells, light emitting diodes, laserdiodes and as a light emitting phosphor material for LEDs and emissiveEL displays.

A second aspect of the invention provides a method of making asemiconductor nanoparticle, the method comprising:

-   -   reacting at least one source of a group II element, at least one        source of a source of a group III element, and at least one        source of nitrogen.

The semiconductor nanoparticle may be composed of a material having theformula II-III-N, where II denotes one or more elements in Group II ofthe periodic table and III denotes one or more elements in Group III ofthe periodic table.

The method may comprise reacting the at least one source of a group IIelement, the at least one source of a source of a group III element, andthe at least one source of nitrogen element in a solvent.

The at least one source of a group II element may comprise a carboxylateof a group II element, and more particularly may comprise a stearate ofa group II element (eg zinc stearate, in the case of formation of ananocrystal having zinc as its group II element, as or one of its groupII elements).

It has been found that the use of a carboxylate, for example a stearate,as a starting material to provide a group II element of the II-III-Ncompound is effective in obtaining a light-emissive II-III-N material,in particular obtaining light-emissive II-III-N nanoparticle.

The nanoparticles increase in size as the reaction progresses so it ispossible to vary the dimensions of the obtained nanoparticles by varyingthe time at which the nanoparticles are extracted from the reactionmixture. Since properties of the nanoparticles such as peak emissionwavelength depend on the nanoparticle dimensions, this enablesnanoparticles having desired properties, for example desired emissive orabsorption properties, to be obtained.

Since the nanoparticles increase in size as the reaction progresses, itis possible to obtain a monodisperse, or substantially monodisperse,population of nanoparticles by extracting all nanoparticles in thepopulation from the reaction mixture at the same time. (As is known, acollection of particles are referred to as “monodisperse”, or“monosized”, if they have the same size and shape as one another.)

A third aspect of the invention provides a method of making asemiconductor nanoparticle, the method comprising:

-   -   reacting at least one source of a group II element and at least        one source of nitrogen.

The semiconductor nanoparticle may be composed of a material having theformula II-N, where II denotes one or more elements in Group II of theperiodic table.

The method may comprise reacting the at least one source of a group IIelement and the at least one source of nitrogen in a solvent.

The at least one source of a group II element may comprise a carboxylateof a group II element, and more particularly may comprise a stearate ofa group II element (eg zinc stearate, in the formation of a II-III-Nnanocrystal having zinc as its group II element, as or one of its groupII elements.

In both the second and third aspects the at least one source of nitrogenmay comprise an amide, for example sodium amide. The use of acarboxylate as a source of a group II element (for example use of zincstearate in an example where zinc is the/a Group II material) togetherwith the use of an amide as the source of a group V element has beenfound to be particularly advantageous in the formation of nanocrystalsof a II-III-V compound, as the carboxylate is believed to help tosolubilise the sodium amide in the reaction mixture to provide a morehomogeneous solution, which is expected to allow for more controlledgrowth of the nanocrystals.

The invention is not however limited to use of a carboxylate as thesource of the group II element and other sources of the group II elementmay be used, such as, for example, amines, acetoacetonates, sulfonates,phosphonates, thiocarbamates or thiolates.

The II-III-N or II-N material may form the core of a core-shellnanoparticle, and the method may further comprise forming a layer ofanother semiconductor material over the core to form the shell. Theanother semiconductor material may be another II-III-N or II-N material,or alternatively the another semiconductor material may be a materialthat is not a II-III-N or II-N material.

Alternatively the II-III-N or II-N material may form the shell of acore-shell nanoparticle, in which case the method comprises forming theII-III-N or II-N material over a core so that the II-III-N or II-Nmaterial forms a shell. The core may be formed of another II-III-N orII-N material, or alternatively the core may be formed of asemiconductor material that is not a II-III-N or II-N material.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be described by wayof example with reference to the accompanying figures, in which:

FIG. 1: shows PL emission spectra of a set of zinc gallium nitridenanocrystal solutions obtained from a single reaction at differenttimes.

FIG. 2: shows the room temperature PL emission spectra of ZnGaNnanocrystal solutions containing having gallium:zinc molar ratios of1:3, 1:1 and 3:1.

FIG. 3 shows the variation in the peak PL emission wavelengths of ZnGaNnanocrystal solutions obtained for different reaction times and usingdifferent zinc to gallium ratios.

FIG. 4: shows the room temperature PL emission spectra of ZnInNnanocrystal solutions obtained from a single reaction at differenttimes.

FIG. 5 shows the variation in the peak PL emission wavelengths of ZnInNnanocrystal solutions obtained for different reaction times and usingdifferent zinc to indium ratios.

FIG. 6: shows the room temperature PL emission spectra of ZnAlNnanocrystal solutions obtained from a single reaction at differenttimes.

FIG. 7: shows the room temperature PL emission spectra of zinc nitridenanocrystal solutions obtained from a single reaction at differenttimes.

FIGS. 8( a) and 8(b) are Transmission Electron Micrographs of ZnAlNnanoparticles obtained by a method of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention relates to nanoparticles, for example nanocrystals, ofsemiconducting compounds. More specifically it relates to nanoparticles,for example nanocrystals, of group II-III-N compound semiconductors ofthe general formulae II-III-N or II-N where II is an element, orelements, from group II of the periodic table, III is an element, orelements from group III of the periodic table and N is nitrogen.

The present invention makes possible the fabrication of nanoparticles,for example nanocrystals. The nanocrystals may be fabricated such thattheir diameters range from about 1 nm to about 100 nm and morespecifically from about 1 nm to about 30 nm. The invention may be usedto fabricate nanocrystals of a range of shapes such as roughly sphericalor teardrop-shapes. In addition the nanocrystals provided by thisinvention may have a core-shell structure where a shell of a secondmaterial is grown directly onto the surface of the nanocrystal (whichforms the core of the core-shell structure). More than one such shellmay be grown. This shell may be made the same material or from adifferent material to that used for the core or an alternative III-V orII-VI semiconductor or any other suitable material. Ideally the band gapof the shell material will be larger that that of the material whichforms the core to help confine the excited state within the core of thenanocrystals; this is known to improve the intensity of the emissionfrom such materials.

In a preferred embodiment, the present II-III-N semiconductornanoparticles may exist in the form of crystalline nanoparticles.

In another preferred embodiment, the present II-III-N semiconductornanoparticles may exist in the form of polycrystalline nanoparticles.

In another preferred embodiment, the present II-III-N semiconductornanoparticles may exist in the form of amorphous nanoparticles.

In another preferred embodiment, the II-III-N nanoparticles may be lightemissive and have a photoluminescence quantum yield of at least 5%, orof at least 20%, or of at least 50%.

In another preferred embodiment, the present II-III-N semiconductornanocrystals consist of zinc gallium nitride. This material alloy has anenergy gap of between 1.0 eV and 3.4 eV, depending on the Zn:Ga ratio,which traverses the visible spectral region.

In another preferred embodiment, the present II-III-N semiconductornanocrystals consist of zinc aluminum gallium indium nitride. Thismaterial has an energy gap of between 0.6 eV and 4.0 eV, again dependingon the exact composition, that traverses the solar spectral region.

In another preferred embodiment, the present II-III-N semiconductornanocrystals consist of zinc aluminum nitride. This material alloy canyield a wide energy gap up to 6.2 eV for emission of ultraviolet light

In another preferred embodiment, the present II-III-V semiconductornanocrystals consist of zinc indium nitride. This material alloy canyield a small energy gap of 0.6 eV for emission of infrared light.

In another preferred embodiment the II-III-N semiconductor nanocrystalscan be doped with one or more impurity elements. Examples of impurityelements are silicon, magnesium, carbon, beryllium, calcium, germanium,tin and lead.

An application of the novel material of the current invention is the useof II-III-N compound semiconductor nanocrystals to provide a phosphorwhich is excited by a light source such as a light emitting diode orlaser diode.

An application of the novel material of the current invention is the useof II-III-N compound semiconductor nanocrystals to provide large areaillumination panels which are excited by a light source such as a lightemitting diode or laser diode.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals in a solar cell.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals in aphotovoltaic device.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals in a lightemitting diode.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals in a lightemitting device.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals in a laser diodedevice.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals in a laser

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals in an electronicdevice.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals in a transistordevice.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals in amicroprocessor device.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals in an amplifierdevice.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals in a powerswitching device.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals in a powerregulator device.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals in a lightdetecting device.

A further application of the novel material of the current invention isthe use of an II-III-N compound semiconductor nanocrystals to providefluorescent fibres, rods, wires and other shapes.

A further application of the novel material of the current invention isthe use of an electrical current to generate the excited state whichdecays with the emission of light to make a light emitting diode withdirect electrical injection into the II-III-N semiconductornanocrystals.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals as part of theback light used in a liquid crystal display.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals as the emissivespecies in a display such as a plasma display panel, a field emissiondisplay or a cathode ray tube.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals as the emissivespecies in an organic light emitting diode.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals as the emissivespecies in a solar concentrator, where the light emitted by the solarconcentrator is matched to a solar cell used to convert the collectedlight to an electrical current. More than one such concentrator may bestacked on one another to provide light at a series of wavelengths eachmatched to a separate solar cell.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals as the lightharvesting species in an organic solar cell or photo detector.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals as the lightharvesting species in a dye sensitised solar cell or photo detector.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals to generatemultiple excitons from the absorption of a single photon though theprocess of multiple exciton generation in a solar cell or photodetector.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals to assistidentification in combat.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals to assist inasset tracking and marking.

A further application of nanocrystals of this invention is the use ofII-III-N compound semiconductor nanocrystals as counterfeit inks.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals as bio markersboth in-vivo and in-vitro.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals in photodynamictherapy.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals as bio markersin for example cancer diagnosis, flow cytometry and immunoassays.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals in flash memory.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals in quantumcomputing.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals in dynamicholography.

A further application of the novel material of the current invention isthe use of II-III-N compound semiconductor nanocrystals in athermoelectric device.

A further application of the novel material of this invention is the useof II-III-N compound semiconductor nanocrystals in a device used intelecommunications.

A further application of the novel material of this invention is the useof II-III-N compound semiconductor nanocrystals for any application.

EXAMPLES

In the following examples, several methods of fabricating a form of thepresent invention are described. Other methods of forming II-III-Nsemiconductor nanoparticles are, but not exclusively: metal organicvapour phase epitaxy (MOVPE), molecular beam epitaxy (MBE), chemicalvapour deposition (CVD), sputtering, plasma assisted vacuum deposition,pulsed laser deposition (PLD), Hydride vapour phase epitaxy (HVPE),sublimation, thermal decomposition and condensation, annealing, powderor metal nitridation.

Photoluminescence quantum yield (PLQY) measurements are carried outusing the procedure described in Analytical Chemistry, Vol. 81, No. 15,2009, 6285-6294. Dilute samples of the nitride nanocrystals incyclohexane with absorbance between 0.04 and 0.1 are used. Nile red PLQY70% (Analytical Biochemistry, Vol. 167, 1987, 228-234) in 1,4-dioxanewas used as a standard.

It should understood that the examples are given by way of illustrationonly, and that the invention is not limited to the examples. Forexample, although Examples 1 to 8 use a carboxylate, in particular astearate, as the source of the group II element the invention is notlimited to this and other precursors of the group II element may beused, such as, for example, amines, acetoacetonates, sulfonates,phosphonates, thiocarbamates or thiolates. Moreover, although Examples 1to 8 use 1-octadecene or dipheyl ether as a solvent the invention is notlimited to these particular solvents.

The methods described below have been found effective to obtainnanoparticles having three dimensions of the order of 1 to 100 nm, orhaving three dimensions of the order of 1 to 30 nm. The size of theobtained nanoparticles may be determined in any suitable way such as,for example, taking a Transmission Electron Micrograph (TEM) image ofthe nanoparticles and estimating the size of the nanoparticles from theTEM image.

Example 1 Colloidal ZnGaN Semiconductor Nanocrystals

Gallium iodide (270 mg, 0.6 mmol), sodium amide (500 mg, 12.8 mmol),hexadecane thiol (308 μl, 1.0 mmol), zinc stearate (379 mg, 0.6 mmol)and 1-octadecene (20 ml) were heated rapidly to 250° C. and maintainedat that temperature. Of the reaction constituents, Gallium iodideprovided a Group III metal (Gallium), sodium amide provided the Nitrogenatoms, hexadecane thiol is a capping agent with an electron-donatinggroup, zinc stearate provided a Group II metal (Zinc) and 1-octadeceneacts as a solvent. Over the course of 60 minutes a number of 0.25 mlportions of the reaction mixture were removed and diluted with toluene(3 ml) and any insoluble materials were removed using a centrifuge. Theresulting clear solutions were analysed by emission spectroscopy andshowed a change in the peak emission wavelength from 450-600 nm over thecourse of the reaction, as shown in FIG. 1. The peak in the emissionspectrum has a full width at half the maximum intensity of the order of100 nm.

The resultant ZnGaN nanoparticles were found to have a Ga:Zn ratio ofapproximately 1:1.3.

When samples from such a reaction are illuminated with a UV lightsources, the resultant emission is easily visible with the naked eye forsamples emitting in the visible region. This illustrates the highquantum yield of ZnGaN nanostructures obtainable by the presentinvention.

The corresponding emission spectra of these samples are shown in FIG. 1.The lefthand-most emission spectrum (shown as a dashed line) wasobtained for a sample of the reaction mixture removed a few minutesafter the start of the reaction, in this example 10 minutes after thestart of the reaction. The righthand-most emission spectrum (shown as adotted line) was obtained for a sample of the reaction mixture removedapproximately one hour after the start of the reaction. The emissionspectra between the lefthand-most emission spectrum and therighthand-most emission spectrum were obtained for samples of thereaction mixture removed at intermediate times.

It should be noted that the peak wavelength of the emission spectrumdoes not change uniformly with time. Initially the peak emissionwavelength increases rapidly with time, but as the reaction proceeds therate of increase, with time, of the peak emission wavelength falls.

As can be seen from FIG. 1, the emission spectra of samples removed attimes up to about one hour after the start of the reaction span much ofthe visible region from blue to orange-red. Thus, nanocrystals havingparticular optical properties (such as a desired peak emissionwavelength) can be obtained by appropriate choice of the reaction periodbefore the nanocrystals are recovered from the solution.

The photoluminescence quantum yield of a sample removed from thisreaction was measured and gave a value of greater than 30%.

Using the same synthesis procedure, several other ZnGaN nanocrystalcompounds were formed. For example:

The ratio of gallium iodide to zinc stearate was varied in order toproduce compounds of zinc gallium nitride containing different amountsof gallium and zinc. FIG. 2 shows the PL spectra from samples made withdifferent zinc to gallium ratios. The emission spectra for nanoparticleswith a Ga:Zn ratio of 3:1 was obtained for a sample of the reactionmixture removed approximately 90 minutes after the start of thereaction, and the emission spectrum for nanoparticles with a Ga:Zn ratioof 1:1 was also obtained for a sample of the reaction mixture removedapproximately 90 minutes after the start of the reaction. The emissionspectra for nanoparticles with a Ga:Zn ratio of 1:3 was obtained for asample of the reaction mixture removed approximately 20 minutes afterthe start of the reaction. Thus, the emission spectra of samples removedat times up to about 90 minutes were found to span theultraviolet-visible-infrared regions.

FIG. 3 shows the variation in the peak PL emission wavelengths of ZnGaNnanocrystals obtained for different reaction times and using threedifferent zinc to gallium ratios. This result demonstrates thatnanocrystals having particular optical properties (such as a desiredpeak emission wavelength) can be obtained by appropriate choice of thereaction period before the nanocrystals are recovered from the solution,and from the appropriate choice of quantities of zinc and gallium in thesynthesis reaction. Thus, as an example, a person wishing to fabricatenanoparticles having a peak emission wavelength of approximately 450 nm(in the blue region of the spectrum) may see from FIG. 3 that this madebe done by fabricating ZnGaN nanoparticles as described in Example 1, bychoosing the quantities of the constituents such that the nanoparticleshave a Ga:Zn ratio of 3:1, and removing the sample from the reactionabout 35 minutes after the start of the reaction.

For a nanocrystal sample made with a Ga:Zn ratio of 4:1 in the reactionconstituents a photoluminescence quantum yield value of 45% was obtainedusing a reaction time of 40 minutes.

It can therefore be seen that the present invention makes possible theformation of zinc gallium nitride nanocrystals, or more generally,nanocrystals of the Group II-III-N compound semiconductor family, whichhave extremely good light-emissive properties.

Example 2 Colloidal ZnInN Semiconductor Nanocrystals

Indium iodide (300 mg, 0.6 mmol), sodium amide (500 mg, 12.8 mmol),hexadecane thiol (308 μl, 1.0 mmol), zinc stearate (379 mg, 0.6 mmol)and diphenyl ether (20 ml) were heated rapidly to 250° C. and maintainedat that temperature. Of the reaction constituents,

Indium iodide provided a Group III metal (indium), sodium amide providedthe Nitrogen, hexadecane thiol is a capping agent with anelectron-donating group, zinc stearate provided a Group II metal (Zinc)and diphenyl ether acts as a solvent. Over the course of 60 minutes anumber of 0.25 ml portions of the reaction mixture were removed anddiluted with cyclohexane (3 ml) and any insoluble materials were removedusing a centrifuge. The resulting clear solutions were analysed by PLemission spectroscopy and showed a change in the maximum emissionwavelength from 500-850 nm over the course of the reaction, as shown inFIG. 4. (The lefthand-most emission spectrum in FIG. 4 was obtained fora sample of the reaction mixture removed approximately 5 minutes afterthe reaction started, and the other emission spectra were obtained forsamples of the reaction mixture removed approximately 10 minutes, 15minutes, 20 minutes, 25 minutes, 35 minutes and 60 minutes after thereaction started.) The peak in the emission spectrum has a full width athalf the maximum intensity of the order of 100 nm.

When samples from such a reaction are illuminated with a UV lightsources, the resultant emission is easily visible with the naked eye forsamples emitting in the visible region. This illustrates the highphotoluminescence quantum yield of ZnInN nanostructures obtainable bythe present invention.

The corresponding PL emission spectra of these samples are shown in FIG.4. The emission spectra of samples removed at times up to about one hourspan substantially the whole visible region and extend into theinfra-red. Thus, nanocrystals having particular optical properties (suchas a desired peak emission wavelength) can be obtained by appropriatechoice of the reaction period before the nanocrystals are recovered fromthe solution.

The photoluminescence quantum yield of a sample removed from thisreaction was measured and gave a value of 10%.

Using the same synthesis procedure, several other ZnInN nanocrystalcompounds were formed. For example:

The ratio of indium iodide to zinc stearate was varied in order toproduce compounds of zinc indium nitride containing different amounts ofindium and zinc. FIG. 5 shows the variation in the peak PL emissionwavelengths of ZnInN nanocrystals obtained for different reaction timesand using different zinc to indium ratios. This result demonstrates thatnanocrystals having particular optical properties (such as a desiredpeak emission wavelength) can be obtained by appropriate choice of thereaction period before the nanocrystals are recovered from the solution,and from the appropriate choice of quantities of zinc and indium in thesynthesis reaction.

For a nanocrystal sample made with a In:Zn ratio of 1:4 aphotoluminescence quantum yield value of 30% was obtained using areaction time of 20 minutes.

It can therefore be seen that the present invention makes possible theformation of zinc indium nitride nanocrystals, or more generally,nanocrystals of the Group II-III-N compound semiconductor family, whichhave extremely good light-emissive properties.

Example 3 Colloidal ZnAlN Semiconductor Nanocrystals

Aluminum iodide (102 mg, 0.25 mmol), sodium amide (468 mg, 12 mmol),hexadecane thiol (259 μl, 1.0 mmol), zinc stearate (474 mg, 0.75 mmol)and 1-octadecene (25 ml) were heated rapidly to 250° C. and maintainedat that temperature. Of the reaction constituents, Aluminum iodideprovided a Group III metal (Aluminum), sodium amide provided theNitrogen atoms, hexadecane thiol is a capping agent with anelectron-donating group, zinc stearate provided a Group II metal (Zinc)and 1-octadecene acts as a solvent. Over the course of 60 minutes anumber of 0.25 ml portions of the reaction mixture were removed anddiluted with toluene (3 ml) and any insoluble materials were removedusing a centrifuge. The resulting clear solutions were analysed byabsorption and emission spectroscopy and showed a change in the maximumemission wavelength from 420-950 nm over the course of the reaction, asshown in FIG. 5. The peak in the emission spectrum has a full width athalf the maximum intensity of the order of 100 nm.

When samples from such a reaction are illuminated with a UV lightsources, the resultant emission is easily visible with the naked eye forsamples emitting in the visible region. This illustrates the highquantum yield of ZnAlN nanostructures obtainable by the presentinvention.

The corresponding emission spectra of these samples are shown in FIG. 6.The lefthand-most emission spectrum in FIG. 6 was obtained for a sampleof the reaction mixture removed a few minutes after the start of thereaction, and the righthand-most emission spectrum was obtained for asample of the reaction mixture removed approximately 60 minutes afterthe start of the reaction. The emission spectra between thelefthand-most emission spectrum and the righthand-most emission spectrumwere obtained for samples of the reaction mixture removed atintermediate times.) The emission spectra of samples removed at times upto about one hour span the ultraviolet to visible region and extend intothe infra-red. Thus, nanocrystals having particular optical properties(such as a desired peak emission wavelength) can be obtained byappropriate choice of the reaction period before the nanocrystals arerecovered from the solution.

The photoluminescence quantum yield of a sample removed from thisreaction was measured and gave a value of greater than 55%.

FIG. 8( a) is a Transmission Electron Micrograph of ZnAlN nanoparticlesobtained by a method as described in this example. The nanoparticleshave a dimension of approximately 3 nm. The image of FIG. 8( a) wasobtained for a sample of the reaction mixture removed approximately 12minutes after the start of the reaction.

FIG. 8( b) is a second Transmission Electron Micrograph of ZnAlNnanoparticles obtained by a method as described in this example. Theimage of FIG. 8( b) was obtained for a sample of the reaction mixtureremoved approximately 60 minutes after the start of the reaction. It canbe seen that the nanoparticles of FIG. 8( b) have a dimension ofapproximately 5 nm, compared to the dimension of approximately 3 nm forthe nanoparticles of FIG. 8( a).

Methods as described herein may be used to fabricate nanoparticleshaving dimensions of more than 5 nm, by using longer reaction times. Itshould however be noted that many of the applications envisaged fornanoparticles of the invention require nanoparticles that emit light inthe visible region of the spectrum and, in general, this requires thatthe nanoparticles have dimensions of 5 nm or below—nanoparticles havingdimensions of more than 5 nm will, in most cases, have a peak emissionwavelength of 750 nm or greater.

Also, fabricating nanoparticles having dimensions of more than 5 nmwould require the use of larger quantities of source chemicals as wellas requiring longer reaction times.

It can therefore be seen that the present invention makes possible theformation of zinc aluminum nitride nanocrystals, or more generally,nanocrystals of the Group II-III-V compound semiconductor family, whichhave extremely good light-emissive properties.

Example 4 Colloidal MgInN Semiconductor Nanocrystals

MgInN nanocrystals were fabricated by a method similar to that describedin example 2, except that magnesium stearate was used as a startingmaterial instead of zinc stearate.

Example 5 Colloidal ZnN Semiconductor Nanocrystals

Sodium amide (500 mg, 12.8 mmol), zinc stearate (379 mg, 0.6 mmol) and1-octadecene (20 ml) were heated rapidly to 250° C. and maintained atthat temperature. Of the reaction constituents, sodium amide providedthe Nitrogen atoms, zinc stearate provided a Group II metal (Zinc) and1-octadecene acts as a solvent. Over the course of 60 minutes a numberof 0.25 ml portions of the reaction mixture were removed and dilutedwith toluene (3 ml) and any insoluble materials were removed using acentrifuge. The resulting clear solutions were analysed by PL emissionspectroscopy and showed a change in the maximum emission wavelength from450-850 nm over the course of the reaction, as shown in FIG. 7. (Thelefthand-most emission spectrum in FIG. 7 was obtained for a sample ofthe reaction mixture removed a few minutes after the start of thereaction, and the righthand-most emission spectrum was obtained for asample of the reaction mixture removed approximately 60 minutes afterthe start of the reaction. The emission spectra between thelefthand-most emission spectrum and the righthand-most emission spectrumwere obtained for samples of the reaction mixture removed atintermediate times.) The peak in the emission spectrum has a full widthat half the maximum intensity of the order of 100 nm.

When samples from such a reaction are illuminated with a UV lightsources, the resultant emission is easily visible with the naked eye forearly stage samples emitting in the visible region. This illustrates thehigh quantum yield of ZnN nanostructures obtainable by the presentinvention.

The corresponding emission spectra of these samples are shown in FIG. 7.The emission spectra of samples removed at times up to about one hourspan from ultraviolet through the whole visible region and extend intothe infra-red. Thus, nanocrystals having particular optical properties(such as a desired peak emission wavelength) can be obtained byappropriate choice of the reaction period before the nanocrystals arerecovered from the solution.

The photoluminescence quantum yield of a sample removed from thisreaction was measured and gave a value of 25%.

It can therefore be seen that the present invention makes possible theformation of zinc nitride nanocrystals, in particular nanocrystals ofthe Group II-N compound semiconductor family, which have extremely goodlight-emissive and crystalline properties.

Example 6 Colloidal ZnInGaN Core with ZnGaN Shell SemiconductorNanocrystals

Gallium iodide (113 mg, 0.25 mmol), indium iodide (124 mg, 0.25 mmol),sodium amide (390 mg, 10 mmol), hexadecane thiol (153 μl, 0.5 mmol),zinc stearate (316 mg, 0.5 mmol) and 1-octadecene (40 ml) were heatedrapidly to 225° C. After 20 minutes the mixture was cooled to roomtemperature and centrifuged to remove any insoluble material. Thismixture consisted of the core only ZnInGaN nanoparticles. To form theZnGaN shell around the nanoparticle core, 20 ml of the core solution wasfurther treated with gallium iodide (113 mg, 0.25 mmol), zinc stearate(316 mg) and sodium amide (185 mg, 5 mmol) and heated to 225° C. for 20minutes.

When samples from such a reaction are illuminated with a UV lightsources, the resultant emission is easily visible with the naked eye forsamples emitting in the visible region. This illustrates the highquantum yield of ZnInGaN—ZnGaN nanostructures (that is, nanostructureswith a ZnInGaN core and a ZnGaN shell) obtainable by the presentinvention. The photoluminescence quantum yield of a sample removed fromthis reaction was measured and gave a value of 30%.

Example 7 Colloidal ZnInGaN Core with ZnS Shell SemiconductorNanocrystals

Gallium iodide (113 mg, 0.25 mmol), indium iodide (124 mg, 0.25 mmol),sodium amide (390 mg, 10 mmol), hexadecane thiol (153 μl, 0.5 mmol),zinc stearate (316 mg, 0.5 mmol) and 1-octadecene (40 ml) were heatedrapidly to 225° C. After 20 minutes the mixture was cooled to roomtemperature and centrifuged to remove any insoluble material. Thismixture consisted of the core only ZnInGaN nanoparticles. To form theZnS shell around the nanoparticle core the highly coloured solution wasdecanted from the solids and a 4 ml sample was treated with zincdiethyldithiocarbamate (100 mg, 0.27 mmol) for 40 minutes at 175° C.

When samples from such a reaction are illuminated with a UV lightsources, the resultant emission is easily visible with the naked eye forsamples emitting in the visible region. This illustrates the highquantum yield of ZnInGaN—ZnS nanostructures (that is, nanostructureswith a ZnInGaN core and a ZnS shell) obtainable by the presentinvention. The photoluminescence quantum yield of a sample removed fromthis reaction was measured and gave a value of 23%.

Example 8 Colloidal ZnInGaN Core with Double Shell of ZnGaN and ZnSSemiconductor Nanocrystals

Gallium iodide (113 mg, 0.25 mmol), indium iodide (124 mg, 0.25 mmol),sodium amide (390 mg, 10 mmol), hexadecane thiol (153 μl, 0.5 mmol),zinc stearate (316 mg, 0.5 mmol) and 1-octadecene (40 ml) were heatedrapidly to 225° C. After 20 minutes the mixture was cooled to roomtemperature and centrifuged to remove any insoluble material. Thismixture consisted of the core only ZnInGaN nanoparticles. To form theZnGaN inner shell around the nanoparticle core, 20 ml of the resultingsolution was further treated with gallium iodide (113 mg, 0.25 mmol) andsodium amide (185 mg, 5 mmol) and heated to 225° C. for 20 minutes. Theresulting solution was centrifuged to remove any insoluble material andthen treated with zinc diethyldithiocarbamate (500 mg, 1.35 mmol) andheated to 175° C. for a period of 60 minutes to form the ZnS outershell.

When samples from such a reaction are illuminated with a UV lightsources, the resultant emission is easily visible with the naked eye forsamples emitting in the visible region. This illustrates the highquantum yield of ZnInGaN—ZnGaN—ZnS nanostructures (that is,nanostructures with a ZnInGaN core and a double shell of ZnGaN and ZnS)obtainable by the present invention. The photoluminescence quantum yieldof a sample removed from this reaction was measured and gave a value of22%.

In Examples 6 to 8 the core, and optionally the shell, of the core-shellnanoparticles of these examples are made of a II-III-N or II-N material.In a further application of the invention, the invention may be used toprovide a shell of a II-III-N or II-N material in a core-shellnanoparticle in which the core is not composed of a II-III-N or II-Nmaterial.

1. A semiconductor nanoparticle composed of a first compound having theformula II-N or II-III-N, where II denotes one or more elements in GroupII of the periodic table and III denotes one or more elements in GroupIII of the periodic table.
 2. A semiconductor nanoparticle as claimed inclaim 1, wherein the nanoparticle is composed of a compound having theformula II-III-N.
 3. The semiconductor nanoparticle as claimed in claim1, wherein the nanoparticle is composed of a compound having the formulaII-N.
 4. A semiconductor nanoparticle as claimed in claim 2, wherein thenanoparticle is composed of ZnGaN.
 5. A semiconductor nanoparticle asclaimed in claim 2, wherein the nanoparticle is composed of ZnInN.
 6. Asemiconductor nanoparticle as claimed in claim 2, wherein thenanoparticle is composed of ZnAlN.
 7. A semiconductor nanoparticle asclaimed in claim 2, wherein the nanoparticle is composed of ZnGaInN. 8.A semiconductor nanoparticle as claimed in claim 2, wherein thenanoparticle is composed of MgInN.
 9. A semiconductor nanoparticle asclaimed in claim 3, wherein the nanoparticle is composed of ZnN.
 10. Asemiconductor nanoparticle as claimed in claim 1 wherein the first II-Nor II-III-N compound is single crystal in structure.
 11. A semiconductornanoparticle as claimed in any claim 1 wherein the first II-N orII-III-N compound is polycrystalline in structure.
 12. A semiconductornanoparticle as claimed in claims 1 wherein the first II-N or II-III-Ncompound is amorphous in structure.
 13. A semiconductor nanoparticle asclaimed in claim 1, wherein the first compound having the formula II-Nor II-III-N forms a core of the nanoparticle and wherein thenanoparticle further comprises a layer disposed around the core andcomposed of a semiconductor material having a different composition tothe first II-N or II-III-N compound.
 14. A semiconductor nanoparticle asclaimed in claim 13, wherein the layer is composed of a second II-N orII-III-N compound, the second II-N or II-III-N compound having adifferent composition to the first II-N or II-III-N compound.
 15. Asemiconductor nanoparticle as claimed in claim 1 wherein thesemiconductor nanoparticle is light emissive.
 16. A semiconductornanoparticle as claimed in claim 15 and having a photoluminescencequantum yield of at least 5%.
 17. A semiconductor nanoparticle asclaimed in claim 15 and having a photoluminescence quantum yield of atleast 20%.
 18. A semiconductor nanoparticle as claimed in claim 15 andhaving a photoluminescence quantum yield of at least 50%.
 19. A methodof making a semiconductor nanoparticle, the method comprising: reactingat least one source of a group II element, at least one source of asource of a group III element, and at least one source of nitrogen. 20.A method as claimed in claim 19 wherein the semiconductor nanoparticleis composed of a material having the formula II-III-N, where II denotesone or more elements in Group II of the periodic table, and III denotesone or more elements in Group III of the periodic table.
 21. A method asclaimed in claim 19 and comprising reacting the at least one source of agroup II element, the at least one source of a source of a group IIIelement, and the at least one source of nitrogen element in a solvent.22. A method of making a semiconductor nanoparticle, the methodcomprising: reacting at least one source of a group II element and atleast one source of nitrogen.
 23. A method as claimed in claim 22wherein the semiconductor nanoparticle is composed of a material havingthe formula II-N, where II denotes one or more elements in Group II ofthe periodic table.
 24. A method as claimed in claim 23 and comprisingreacting the at least one source of a group II element and the at leastone source of nitrogen element in a solvent.
 25. A method as claimed inclaim 19; wherein the at least one source of a group II elementcomprises a carboxylate of a group II element.
 26. A method as claimedin claim 25 wherein the at least one source of a group II elementcomprises zinc stearate.
 27. A method as claimed in claim 19 wherein theat least one source of nitrogen comprises an amide.
 28. A method asclaimed in claim 22; wherein the at least one source of a group IIelement comprises a carboxylate of a group II element.
 29. A method asclaimed in claim 28 wherein the at least one source of a group IIelement comprises zinc stearate.
 30. A method as claimed in claim 22wherein the at least one source of nitrogen comprises an amide.